1. Field of the Invention
The present invention relates to a method of preparing carbon nanotube complexes and, more particularly, to a method of filling carbon nanotubes with materials such as metal particles, metal compounds, or a combination thereof.
2. Description of Related Art
A nano carbontube is a hollow tubule constituted from carbon atoms. The recent discovery and bulk synthesis of nano carbontubes has led to much speculation about possible uses of these graphic structures. Broughton and Pederson predicted on the basis of computer simulations that open nanotubes may be filled with liquid by capillary suction. In 1993, P. M. Ajayan and Sumio Iijima proved that the prediction is practicable by annealing nanotubes in the presence of liquid lead, which involved the opening of the tube ends, keeping them at 400° C. and subsequently filling of the tubes with material through capillary suction. However, only portions of nanotubes were filled with the desired material, and the uniformity of the distribution of those materials was unsatisfactory.
In 1994, C. Guerret-Plécourt et al. used capillary suction and successfully filled the tubes with several materials for forming continuous nanowires. Meanwhile, they investigated some chosen elements of various physical and chemical properties to separate the factors having a role in the growth mechanism of nanowires in carbon nanotubes (C. Guerret-Plécourt, Y. Le Bouar, A. Lolseau, H. Pascard. Nature 372 (1994) 761-765).
In 1994, D. Ugarte et al. adopted a physical way to fill nanotubes. They annealed nanotubes at several hundreds degrees Celsius and thus obtained nanotubes filled with silver nitrate filament. Other material such as lead oxide (PbO2) have been used, however the reaction needed to be heated to 450° C. or the lead oxide would not enter the nanotubes (D. Ugarte, T. Stöck J. M. Bonard, A. Châtelain, W. A. de Heer. Appl. Phys. A 67 (1998) 101-105).
Filling hollow carbon nanotubes with chosen materials opens new possibilities of generating nearly one-dimensional nanostructures, and the method is generally as described below.
First, nanotubes are opened by oxidation in air; subsequently, the nanotubes are immersed in molten salts, then the materials enter the nanotubes to provide carbon nanotube complexes. Another way to provide carbon nanotube complexes is a wet impregnation method, which takes a long period of time, usually 12 hours or more, for immersing carbon nanotube in a prepared solution. Some further methods utilize catalysts, however many drawbacks occur and the results are inferior.
In the carbon nanotube complexes provided by the prior methods, disadvantages such as insufficient filling (i.e. some part of the cavity remains unfilled), nano-wire breaking (i.e. incontinuous nanowiring), non uniformity, or residue forming on the outer surface of the nanotubes may occur. Also, the prior methods may not be easy to execute because a high annealing temperature is often required and a long period of immersion time is involved. Therefore, it is desirable to provide an improved method to mitigate the aforementioned problems.